Papers by Keyword: DTA Analysis

Abstract: Different amounts of iron oxide (Fe₂O₃) were added into a base calcium alumino-silicate glass (CaO 40, Al₂O₃ 9, SiO₂ 51 wt%). The crystallization behavior of the glassed was investigated by DTA, XRD, SEM and optical microscopy. DTA analysis on the samples with and without the iron additions shows that the iron-containing glasses obviously absorb more heat energy than the base glass. All the glasses show two endothermal peaks correspondent to two transition temperatures, Tg₁ and Tg₂, indicating the existence of phase separation. Compared with the base glass, an initial addition of 5wt% Fe₂O₃ does not result in significant changes in Tg₁, but a large decrease in Tg₂ is observed. Further additions of 10 and 15wt% Fe₂O₃, both Tg₁ and Tg₂ decreases. The iron-containing glasses show two crystallization peaks in their DTA curves. Fe₂O₃ facilitates the crystallization of the calcium alumino-silicate glass indicated by the decreased activation energy and increased Avrami exponent. SEM observations evidenced that the crystallintes in the heat treated samples are nanosized. It is evidenced that the base glass and the glasses containing 5 and 10 wt% Fe₂O₃ are surface crystallized upon heat-treatment and the main crystalline phase is wollastonite. The surface crystallization layer and the grain size increase with Fe₂O₃. However, an addition of 15wt% Fe₂O₃ results in a bulk crystallization leading to the formation of iron-and aluminum-containing phases.

Abstract: Ni based amorphous alloys with Si and B, which can also, contains Fe and Cr, prepared by rapid solidification, have low melting temperatures. This fact increases their susceptibility to be joined by welding and brazing. The glass forming ability (GFA) is conditioned also by the crystallization delay, due to certain chemical composition of the alloys. The thermal stability of these alloys was revealed by DTA analysis and structural characteristics were investigated by XRD. Applying an annealing at temperatures between 420°C and 540°C, with 30 minutes maintaining time, allowed the investigation of phase occurred during the crystallization and the estimation of the crystalline grains dimensions.

Abstract: The well-aligned growth structures which derive from directional solidification of ceramic eutectics are of great interests due to their potential use in electronic devices and as structural materials at high temperatures. Because of the complexity of the component system and very high melting points, the solidification behavior on the oxide ceramic eutectic is still unclear up to date. In the presented paper, the Al₂O₃-Y₂O₃-ZrO₂ ternary eutectic ceramic is remelted by a DTA apparatus. The maximal heating temperature is 1950 °C. The melting and solidification behavior are investigated by the DTA analysis. The solidification microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The results show that solidus temperature and the liquidus temperature are 1738.4 °C and 1750.1 °C, respectively. The formation path of eutectic phase is discussed. The microstructure of as-solidified eutectic ceramic shows a divorced ternary eutectic structure consisting of Al₂O₃, YAG and ZrO₂ phases with a random distribution. Furthermore, the microstructural comparison with directionally solidified ternary eutectic ceramic is presented and discussed.